1. Technical Field
The present invention relates to a semiconductor device having a nickel silicide layer provided on a silicon substrate, and a method of manufacturing the same.
2. Related Art
There are known conventional techniques of forming a nickel silicide layer on a silicon substrate, such as those described in Japanese Laid-Open Patent Publication Nos. 2004-172571, 9-153616, 2004-319592, 2004-128501 and 7-38104.
In the method described in Japanese Laid-Open Patent Publication No. 2004-172571, a nickel-containing, silicide-forming metal film is formed over the surface of a silicon substrate, and thereafter nitrogen gas and titanium source gas are introduced to thereby form an N-rich (nitrogen-rich) titanium film on the silicide-forming metal film. The stack is then annealed at 200 to 700° C. to thereby form a nickel silicide film. According to this document, the method is successful to remove unreacted metal residue on the surface of the field oxide film and on the surface of the sidewall spacer of a transistor, by virtue of the capping N-rich titanium film.
Japanese Laid-Open Patent Publication No. 9-153616 describes that nickel is sputtered in a mixed gas containing nitrogen gas and argon gas, and the sputtering process is followed by annealing at a temperature of 400 to 700° C. for 30 seconds. According to this document, the resultant NiSi film can be nitrided inside the film, by adjusting the nitrogen concentration in the sputtering gas to 5% or around. It is also reported that sputtering Ni with 5% nitrogen concentration was successful in suppressing junction leakage, when the thickness of the Ni film is adjusted to 30 nm, as compared with the case where the nitrogen concentration was 0%.
Japanese Laid-Open Patent Publication No. 2004-319592 describes that the source/drain region of a p-MOS transistor is implanted with Ge ion, before nickel silicide is formed. It is also described that the Ge implantation process is followed by sequential formation of a Ni film of about 10 nm thick and TiN film of about 10 nm, over the surface of the substrate, and annealing at 300 to 600° C. so as to form a Ni monosilicide film having a thickness of about 20 to 25 nm. It is therefore concluded that Ni monosilicide is formed both for the p-MOS transistor and n-MOS transistor, and thereby the variation of the transistor characteristics can be suppressed.
Japanese Laid-Open Patent Publication No. 2004-128501 describes a method to improve adhesion between a nickel silicide layer and a capping silicon nitride layer. According to this document, nickel silicide is formed on a silicon substrate by the two-step annealing process, wherein a Ni film is deposited over the surface of the substrate, the substrate is annealed in a first step at 260 to 310° C., titanium nitride is deposited on the substrate, and then annealed in a second step at 400 to 550° C. In the first step, a nickel-rich alloy is formed, and then the residual nickel is removed. By forming the titanium nitride film thereafter, nitrogen in the titanium nitride film is reportedly fused with the surface of nickel monosilicide in the second step, to thereby protect the underlaid nickel silicide. After the titanium nitride film is removed from the surface of the nickel silicide layer, a silicon nitride capping film is deposited. The silicon nitride film is conventionally used as interlayer isolation film. It is described that the above-mentioned process flow is effective to prevent the formation of a silicon-rich film between the nickel silicide and the silicon nitride film, and thereby the adhesion between the nickel silicide and the silicon nitride film can be improved.
This document also describes that the substrate, having the nickel layer and a titanium nitride capping layer covering the nickel layer formed thereon, is heated up to approximately 290° C., the titanium nitride layer and the residual nickel layer are removed, and the substrate is annealed at around 500° C.
Japanese Laid-Open Patent Publication No. 7-38104 describes consecutive sputtering of Ni and TiN on the surface of a wafer. It is described that the surface of Ni silicide is nitrided by providing TiN on Ni. More specifically, it is shown that nitrogen is contained in Ni silicide in a region thereof deeper than 5 nm from the surface of Ni silicide. Due to the nitride film, a reaction forming insulator film between Ni silicide and oxygen is prevented even if it is heated up to 350° C. in oxygen atmosphere.
In this document, it is also described that a similar effect can be obtained also by two-step annealing after forming the Ni film, and then forming TiN. Temperatures of the two-step annealing are reportedly 300 to 400° C., and 400 to 500° C., respectively.
Although differed in the technical field, Published Japanese Translation of PCT International Publication for Patent Application No. 2005-522035 describes a method of forming cobalt silicide. According to this document, first a cobalt layer is formed on silicon. A titanium nitride layer of 10 to 100 nm thick is formed thereon under nitrogen gas supply, the nitrogen supply is then interrupted, and a titanium layer of 10 to 30 nm is formed. The titanium layer plays a role of a getter layer reactive with oxygen atom or the like, in the succeeding annealing step.